(CNN) -- Voters in El Salvador will line up at a crossroads of history Sunday, deciding whether to give the presidency to a political party that 17 years ago was waging guerrilla war on the government.

Although polls indicate that the race has tightened considerably, most analysts say that Mauricio Funes, the candidate of the former guerrilla group known as FMLN, is still slightly favored to beat ARENA party hopeful Rodrigo Avila. That would end a 20-year hold on the presidency by the right-leaning ARENA.

"It's a sign that there's democracy in that country, which is something the United States tried to foster," said Bernard Aronson, who as President George H.W. Bush's assistant secretary of state for inter-American affairs from 1989-93 was heavily involved in ending El Salvador's 12-year civil war.

The FMLN, which is the Spanish acronym for the Farabundo Marti National Liberation Front, was formed in late 1980 as an umbrella group for five leftist guerilla organizations fighting a U.S.-backed military dictatorship. The guerrillas and the government signed a peace pact in 1992, and the FMLN became a legitimate political party.

By some estimates, 75,000 Salvadorans died during the war.

The new president will find "a country that still retains a lot of bitterness, a lot of division," said Peter Hakim, president of the Washington-based Inter-American Dialogue policy institute.

The election, Hakim said, "is an important test of how far El Salvador has come."

The result also will be an important test of how far El Salvador will go.

With an economy in deep trouble and neither party having enough seats to control the national Legislative Assembly, much will depend on the party that loses.

"Conflict occurs when one person wants to force a conflict," Hakim said. "Compromise requires both sides."

No one is certain what will happen if ARENA loses.

"That's a big unknown," said Heather Berkman, a Latin America analyst with the consulting firm Eurasia Group. "I still think they'll play ball. They have an incentive to get along with the new administration. They certainly don't want to be shut out of the process."

Otto Reich, who served in high-level Latin American posts for President Reagan as well as George H.W. Bush and George W. Bush, sees the possibility of a spirited fight from ARENA.

"If I had to guess, I'd say ARENA will try to put democratic obstacles in the way of an FMLN consolidation of power," Reich said.

Although ARENA, which are the Spanish initials for the Nationalist Republican Alliance, has come back from a 14-point deficit in some polls two months ago, Reich says that winning a fifth consecutive term is "swimming against the tide."

"People in El Salvador are weighing risks and opportunities," Reich said. "They have an opportunity to replace a party with which they have gotten tired."

Hakim also sees voter fatigue with ARENA, saying, "One party has managed the country forever and ever."

Undecided voters among the 4.2 million Salvadorans eligible to cast ballots could decide the election.

"It will come down to how about 16 to 20 percent of the people will vote," Berkman said.

Many of those voters will be weighing competing doubts.

"The uncertainty is that the FMLN has never been in power," said Berkman.

But voters also will be asking themselves, she said, whether they are "better off than they were five years ago, 10 years ago? Avila cannot run on a message of change. Funes' message of change and new people in power will be more effective."

Since the war ended, Salvadorans have mostly supported ARENA because of concerns over the FMLN's left-wing agenda and the group's guerrilla background. There also have been outside influences.

"The country has been afraid to vote for the left because of fears from Washington," Larry Birns, director of the nonprofit Council on Hemispheric Affairs, said recently.

With the election of Barack Obama as president, Salvadorans may be more likely to expect a different attitude from Washington.

El Salvador, Colombia and Peru have been the United States' closest allies in Latin America. Birns calls the three nations "Washington's street-corner guys."

With an FMLN victory, El Salvador would join other Latin American countries that have elected leftist leaders in recent years: Venezuela, Bolivia, Nicaragua, Argentina, Honduras, Guatemala, Ecuador and Brazil.

But Berkman and others warn that the United States must not lump everyone together.

"People tend to look at the left in Latin America and oversimplify it," Berkman said. "There's the good left and the bad left."

Or, as Aronson put it, "There's leftists, and there's leftists."

Aronson sees two types of leftist governments in Latin America: "institutional" governments like Brazil's that "have made peace with the free market" while championing social programs and populist, more radical governments like Venezuela's.

Analysts are not sure what to make of Funes, a former freelance journalist for CNN en Espanol who is projecting a moderate image.

"The FMLN did something very clever," Reich said. "They put somebody at the head of the party who is not a guerrilla, not a terrorist."

Even the FMLN may not know what to expect from Funes. Berkman calls it "an issue of uncertainty" between the former journalist and the former guerrilla group.

"There's a lot of unknowns about how the relationship between Funes and the FMLN will proceed," she said, adding that she would watch his Cabinet picks and whether he brought in people from other parties.

A Funes victory would be a defining moment for the FMLN.

"It's an important transformation," Hakim said. "The ex-guerrillas have to make a decision: Are they going to try to bring about revolutionary, radical change or manage the whole country and have step-by-step reform?"

Aronson sees it as "a test of whether they will be pragmatic or ideological."

The FMLN may not have a choice but to be pragmatic. The party holds 35 seats in the 84-member National Assembly. ARENA has 32 seats. Forty-three votes are needed to pass most legislation, and some measures require "supermajority" approval of 56 votes.

That means that if ARENA and the FMLN cannot agree on a measure, they have to look to one of the minor parties for support. The PCN, the National Conciliation Party, has 11 seats and could emerge as a power broker. Two other parties hold six seats.

"It is in the PCN's interest to play ball as well," Berkman said. "The PCN will act as a moderating force."

Berkman also said the FMLN would probably take a moderate approach because the nation relies too much on outside investments and remittances from Salvadorans living abroad for the former guerrillas to adopt too much of a radical approach.

But Hakim worries about something else, should the FMLN oust ARENA.

"I think ARENA may be prepared for this," he said. "I'm concerned that the FMLN may not be prepared to govern."